The present invention relates to a color laser printer, specifically to a color laser printer which makes it possible to stabilize the quality of an image in response to environmental changes.
A printer using an electro-photographic method forms an electrostatic latent image by scanning an electrically charged surface of a photosensitive body using a laser beam, and performs image development by neutralizing the electrostatic latent image using a toner charged with a charge of the opposite polarity. As disclosed in Japanese Patent Application Laid-Open Number 07-128974 (1995), the amount of charge toner particle changes due to the environmental conditions of temperature and humidity. For example, under conditions of high temperature and high humidity, the amount of charge per single toner particle becomes smaller, and under conditions of low temperature and low humidity, the amount of charge per single toner particle becomes larger. Therefore, it should be noted in the general characteristic of the electrophotographic method used in a laser printer that a larger amount of toner is required for neutralizing the electrostatic latent image under an environmental condition of high temperature and high humidity, with the result that the reproduced image will have a higher density than will occur under an environmental condition of low temperature and low humidity.
In order to solve the above problem, it is proposed in Japanese Patent Application Laid-Open Number 07-128974 (1995) is controlling the development apparatus by using a toner density detector and a sensor for detecting temperature and humidity, and Japanese Patent Application Laid-Open Number 6-64238 (1994) proposes a method for correcting the laser intensity and switching the gamma correction tables by using a density sensor mounted on the photosensitive body.
However, in the prior art, since the relation between the number of toner particles and the printing density (lightness or saturation) is not necessarily linear, the control of toner density and the control of the maximum laser intensity may stabilize the whole paint density of the reproduced image, but there still remains a problem in that the intermediate gray level density can not stabilized.
With the method as disclosed in Japanese Patent Application Laid-Open Number 6-64238 (1994) in which a density sensor is mounted on the photosensitive body and the gamma correction tables are switched, since the image output is required for calibration, it is difficult to respond to dynamic changes in the environmental condition promptly. This makes it inconvenient for users to operate an office printer continuously all day long. Even in selecting and switching the gamma correction tables in response to detected parameters of temperature and humidity, many tables are required in order to respond smoothly changes in both the temperature and the humidity. On the other hand, in trying to reduce the number of tables, what is caused is a problem wherein the reproduced image becomes unstable at a transition operating condition at which the tables to be selected are switched.
In the case of color laser printers, as since the characteristics of different color ink materials are different from one another even for the same environmental conditions, and the change in the characteristic for a combination of color ink materials for a color mixture for a change in environmental conditions can not be resolved, which leads to a problem in that a change in the color balance can not be corrected.